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Applied and Environmental Microbiology, July 2004, p. 4048-4052, Vol. 70, No. 7
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.7.4048-4052.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Effect of Dilution Rate on Metabolic Pathway Shift between Aceticlastic and Nonaceticlastic Methanogenesis in Chemostat Cultivation

Toru Shigematsu,1* Yueqin Tang,1 Tsutomu Kobayashi,1 Hiromi Kawaguchi,1 Shigeru Morimura,1 and Kenji Kida1,2

Graduate School of Science and Technology,1 Department of Applied Chemistry and Biochemistry, Faculty of Engineering, Kumamoto University, Kumamoto City, Kumamoto 860-8555, Japan2

Received 23 January 2004/ Accepted 17 March 2004

Acetate conversion pathways of methanogenic consortia in acetate-fed chemostats at dilution rates of 0.025 and 0.6 day–1 were investigated by using 13C-labeled acetates, followed by gas chromatography-mass spectrometry (GC-MS) analysis of the CH4 and CO2 produced. Nonaceticlastic syntrophic oxidation by acetate-oxidizing syntrophs and hydrogenotrophic methanogens was suggested to occupy a primary pathway (approximately 62 to 90%) in total methanogenesis at the low dilution rate. In contrast, aceticlastic cleavage of acetate by aceticlastic methanogens was suggested to occupy a primary pathway (approximately 95 to 99%) in total methanogenesis at the high dilution rate. Phylogenetic analyses of transcripts of the methyl coenzyme M reductase gene (mcrA) confirmed that a significant number of transcripts of the genera Methanoculleus (hydrogenotrophic methanogens) and Methanosarcina (aceticlastic methanogens) were present in the chemostats at the low and high dilution rates, respectively. The mcrA transcripts of the genus Methanosaeta (aceticlastic methanogens), which dominated the population in a previous study (T. Shigematsu, Y. Tang, H. Kawaguchi, K. Ninomiya, J. Kijima, T. Kobayashi, S. Morimura, and K. Kida, J. Biosci. Bioeng. 96:547-558, 2003), were poorly detected at both dilution rates due to the limited coverage of the primers used. These results demonstrated that the dilution rate could cause a shift in the primary pathway of acetate conversion to methane in acetate-fed chemostats.

* Corresponding author. Mailing address: Department of Materials and Life Science, Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto City, Kumamoto 860-8555, Japan. Phone: 81 96 342 3668. Fax: 81 96 342 3679. E-mail: shige{at}kumamoto-u.ac.jp.

Applied and Environmental Microbiology, July 2004, p. 4048-4052, Vol. 70, No. 7
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.7.4048-4052.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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